This invention relates to a low-temperature separation process for removing most of the C.sub.1+ hydrocarbons from a gaseous mixture containing essentially hydrogen, C.sub.1+ -hydrocarbons, and carbon monoxide, the resultant mixture being useful for further processing in a methanol synthesis plant. By C.sub.1+ hydrocarbons is meant gaseous hydrocarbons predominating in methane.
Such a process has been known, for example, from "Linde-Berichte aus Technik und Wissenschaft" [Linde Reports on Science and Technology] 51 : 7-9 (1982). Gas subjected to preliminary purification, i.e. gas freed of CO.sub.2, H.sub.2 S and in some cases COS, is cooled, after adsorptive removal of trace impurities, to such an extent that CO, as well as the associated components Ar, N.sub.2, and CH.sub.4 are condensed out. The condensate is fed to a hydrogen stripper to separate dissolved hydrogen. The degasified condensate is then introduced into a methane-CO separating column. The methane obtained as the sump product is discharged as fuel gas. Pure CO, withdrawn from the head of the separating column, is compressed to the discharge pressure after heating. A CO cycle stream is returned into the process and liquefied. This stream serves, in part, as reflux for the methane-CO separating column and, in part, as refrigerant. In this process, the carbon monoxide contained in the crude gas is obtained separately from hydrogen under reduced pressure, e.g., 5 to 30 bar, and is recompressed to syngas pressure. However, if the CO obtained during the low-temperature separation is to be utilized for methanol synthesis, this represents an additional energy requirement.